I've been finally scared into upgrading my Thermaltake TR2 600w to a possible Corsair HX650v2 650W.
CPU: i5 3570k running stock - will overclock when I upgrade my motherboard
GPU: Gigabyte GTX 670 windforce x3 oc - overclocked MSI Afterburner.
Motherboard: GA-B75M-D3H - I know it's very basic but for now its all I need
HDD: just a 500gb hitachi - don't know the RPM but its basic -
Fan controller: Lamptron FC5
Fans: 5 120mm thermaltake thunderblade red led fans
CPU cooler: Cooler Master V6 GT
Drives: Samsung DVD/CD burner & player.
Lights: 2 BitFenix alchemy red led light strips.
RAM: Corsair vengeance 4GBx2 ddr3 1666MHz dual channel
It's not a bad idea to have an 850W psu but 650W is more than enough for two 670s and an overclocked 3570K.
Look at review from HardOCP, TechPowerUp and XbitLabs. They're all running 2 670s and an overclocked and/or more power hungry CPU and power consumption under load is still below 600W. Your psu will be fine for 2 670s and an overclocked 3570K.